1. Field of the Invention
This invention relates to a gear type of manual transmission for an automotive vehicle, and, more particularly, to a gear type of manual transmission having an improved lubrication system for an automotive vehicle.
2. Description of Related Art
A gear type of manual transmissions connected, for example, to an engine which is installed in an engine compartment of an automotive vehicle with its output shaft directed in the longitudinal direction of the vehicle generally include four shafts, namely input and output shafts arranged in coaxial alignment with each other, a counter shaft arranged in parallel with those input and output shafts, and a reverse idler shaft. Counter or cluster gears of a plurality of gear units are disposed on the counter shaft, and others are disposed on either the input shaft or the output shaft, or the reverse idler shaft.
The manual transmission generally transmits input torque to the counter shaft through a unit of an input gear and a counter reduction gear at a specified reduction ratio and then to the output shaft through selected one of various speed gear units. This manual transmission is called an "Input Reduction Gear Type" because speed reduction is made between the input shaft and the counter shaft. The input reduction gear type of manual transmission has an input gear and a reduction gear fixed to the input shaft and the counter shaft, respectively.
Manual transmissions, which are called an "Output Reduction Gear Type," have a reduction gear unit comprising an output reduction gear and a counter reduction gear fixedly disposed on the output shaft and the counter shaft, respectively, to reduce output torque. Such an output reduction gear type of manual transmission is known from, for example, Japanese Unexamined Patent Publication No. 2-93151. In this type of manual transmission, input torque is transmitted to the counter shaft without being multiplied, and torque applied to each of the counter gears except the counter reduction gear is low consequently. While the transmission has the advantage that the counter gears are made small in diameter and thin, which is always desirable for the transmission to be small in size, nevertheless, various constraints are imposed on the counter reduction gear. Specifically, since torque is reduced by the reduction gear unit before transmitted to the output shaft, the output reduction gear is required to have strength and rigidity higher than the input reduction gear of the input reduction gear type of manual transmission, and consequently required to have a large face width. Due to the output reduction gear which has a large face width and to which large torque is applied, parts of the output shaft and the counter shaft on which the reduction gears are disposed and firmly borne or supported by strong bearing structures. As taught in, for example, Japanese Unexamined Utility Patent Publications Nos. 2-22452 and 2-38736, in order to meet the demand, it is known to use tapered roller bearings, which are capable to withstand both high radial and thrust loads, to support the output shaft and/or the counter shaft on both sides of the reduction gear. Regarding tapered roller bearings used in the transmission, it is known in the art that lubricating oil is easily drawn in a direction of a diameter change from small to large of an inner race of the tapered roller bearing due to a centrifugal force generated by revolutions of the shaft fitted in the inner race.
Further, considering the rotational speed of the counter shaft of the input reduction gear type of conventional manual transmission, it depends upon the gear ratio of a reduction gear unit disposed between the input and counter shafts, and hence lower than the speed of rotation of the input shaft in spite of gears. As against, the rotational speed of the counter shaft of the output reduction gear type of manual transmission depends upon the gear ratio of a selected gear. Accordingly, it is increased higher than that of the input shaft when the selected gear is somewhat higher. In other words, if both types of manual transmissions have reduction gear units of a same gear ratio, the rotational speed of the output reduction gear type of manual transmission is significantly higher than that of the input reduction gear type of manual transmission when specific higher gears are selected. In such a case, the counter reduction gear turns at a significantly high rotational speed.
While the counter shaft rotates at an increased rotational speed, a bearing for any racing gear (which refers to a gear rotating relatively to the shaft on which it is disposed) is put under extremely rigorous lubrication conditions. Especially, a racing gear of a reverse gear unit rotates in an opposite or counter direction to the direction of rotation of the counter shaft by means of the reverse idler gear, the relative speed between the counter shaft and the racing gear becomes extremely higher. Regarding a reverse and a first gear unit which have large reduction ratios, in the case that a smaller gear of the reverse gear unit or the first gear unit is disposed for relative rotation on the input shaft, the relative speed of the small gear with respect to the input shaft is extremely high, putting the bearing of the racing gear, in particular, under extremely rigorous lubrication conditions.
In the gear type of manual transmission, the utilization is made of counter racing gears to splash and supply oil in an oil sump of the transmission housing to mating teeth of gears and bearings for racing gears and their associated moving parts for lubrication. The oil splashes mostly hit against an interior wall of the transmission case and flows down along the wall. During flowing down, the oil looses heat and is cooled to some degree before supplied to those moving parts.
It is necessary to consider effects of stir resistance caused due to rotations of the counter shaft and counter gears to temperature of lubricating oil. In order to decrease the stir resistance to control an increase in oil temperature, it is desirable to reduce the amount of lubricating oil as small as possible within the limits. For the output reduction gear type of manual transmission, in particular, there is a strong demand for decreasing the amount of lubricating oil because, while a higher gear is provided, the rotational speed of the counter gear is higher as compared with that of the input reduction gear type of manual transmission. However, it is hard for the conventional manual transmissions to overcome these somewhat conflicting demands that govern decreasing the amount of lubricating oil and reliable lubrication of moving parts of the transmission.